Nuclear pore complexes occur in all eukaryotes integrated into the nuclear envelope. The so-called dense lamella, located between peripheral heterochromatin and inner membrane of the nuclear envelope may also be ubiquitous in eukaryotesm although its ultrastructural appearance may vary greatly. Little is known on the composition, function, synthesis and turnover of these organelles. It was suggested that they play an important role in nucleocytoplasmic exchange as well as in chromatin organization. Recently we have been able to isolate for the first time, from rat liver nuclei, a fraction which contains the pore complexes and the dense lamella linked to each other. Further subfractionation and subsequent extensive biochemical characterization of the separated components is the main objective of the proposed research. In addition we propose to isolate similar fractions from other cells such as chicken liver, and -erythrocytes, tissue culture cells, plant cells, and from amphibian oocytes. The latter will also be used in an attempt to isolate the so-called annulate lamellae, which are cytoplasmic derivatives of the nuclear envelope, containing numerous pore complexes. Annulate lamellae are frequent in oocytes, spermatocytes and cancer cells. Subfractionation of the components of the annulate lamellae and comparison to those of the nuclear envelope will be attempted.